Soldering methods for SMD components in the soldering process
Soldering process in the SMD components of the welding method
1 before welding on the pads coated with flux, with a soldering iron to deal with once, so as to avoid poor tinning of the pads or oxidized, resulting in bad welding, the chip is generally not required to deal with.
2 with tweezers carefully put the QFP chip on the PCB board, pay attention not to damage the pins. Make it aligned with the pad, to ensure that the chip is placed in the right direction. The temperature of the soldering iron to more than 300 degrees Celsius, the tip of the soldering iron tip Dipped in a small amount of solder, with a tool to press down on the position of the chip has been aligned in the two diagonal position of the pins with a small amount of solder, still press down on the chip, weld the two diagonal position of the pins, so that the chip is fixed and can not be moved. After welding the diagonal to re-check the position of the chip is aligned. If necessary, adjust or remove and re-align the position on the PCB.
3 start soldering all the pins, should be added to the tip of the soldering iron, all the pins will be coated with solder to keep the pins wet. Use the tip of the soldering iron to touch the end of each pin of the chip until you see the solder flowing into the pin. When soldering to keep the tip of the soldering iron and the soldered pins in parallel, to prevent the occurrence of overlap due to excessive solder.
4 After soldering all pins, wet all pins with flux to clean the solder. Wick off excess solder where needed to eliminate any possible shorts and laps. Finally, use tweezers to check for false soldering. Once the inspection is complete, remove the flux from the board by dipping a stiff bristle brush in alcohol and wiping carefully in the direction of the pins until the flux disappears.
5 chip resistive components are relatively easy to weld some, you can first point on a soldering point on the tin, and then put on one end of the component, use tweezers to hold the component, weld one end, and then see if it is put on the right; if it has been put on the right, then welded on the other end. If the pin is very thin in step 2, you can first add tin to the chip pin, and then use tweezers to clamp the core, lightly knocked on the edge of the table, pier in addition to the excess solder, the third step of the soldering iron does not have to tin, soldering iron direct welding. When we complete a circuit board after the welding work, we have to check the quality of the solder joints on the circuit board, repair, refill welding. Meet the following criteria for solder joints
We believe that the solder joints are qualified.
(1) The solder joints into the inner arc (conical).
(2) The whole solder joint should be complete, smooth, no pinholes, no rosin stains.
(3) If there are leads, pins, their exposed pin length should be between 1-1.2MM.
(4) Parts foot profile visible tin dispersion is good.
(5) The solder will surround the entire location of the tin and the foot of the part.
Do not meet the above standards of the solder joints we believe that is unqualified solder joints, the need for secondary repair.
(1) false soldering: seems to be welded in fact not welded, mainly due to dirty pads and pins, flux is not enough or not enough heating time.
(2) short-circuit: foot parts in the foot and foot by the excess of solder connected to the short-circuit, including residual slag so that the foot and foot short-circuit.
(3) off-set: due to the device in the pre-solder positioning is not allowed, or in the welding caused by errors resulting in the pin is not in the specified pad area.
(4) less tin: less tin means that the tin point is too thin, can not be fully covered by the copper skin of the parts, affecting the connection fixed role.
(5) more tin: parts foot completely covered by tin, that is, the formation of the outer arc, so that the shape of the parts and pads can not be seen, can not determine whether the parts and pads on the tin good.
(6) tin ball, tin slag: PCB board surface attached to excess solder ball, tin slag, will lead to small pins short circuit.
